Recently, there is a great demand for miniaturization of electronic equipment such as cellular phones in particular, and circuit boards built into electronic equipment are also required to be smaller, thinner, and higher in mounting density. For example, in Japanese Laid-open Patent 2001-53413, disclosed is a method of manufacturing electronic part built-in boards in which electronic parts are mounted by coating electronic parts in such a manner as to expose a connection of at least one electronic part, and forming a metallic pattern on a resin surface including the exposed connection. Further, a method of manufacturing a multi-layer electronic part built-in board by laminating boards is also disclosed. By using such a configuration, it is possible to greatly reduce size and to improve mounting density of a circuit board.
Further, in Japanese Laid-open Patent 2001-93934, disclosed is a method of forming a circuit pattern with use of conductive paste on a pattern formed surface of a substrate including a circuit connection, inserting a semiconductor integrated circuit element into a substrate, and exposing circuit connections of the semiconductor integrated circuit element on the pattern formed surface of the substrate. Thus, it is possible to prevent the semiconductor integrated circuit element from sinking into the substrate without using anisotropic conductive resin during mounting, to thereby improve productivity and to lower cost, and further, to prevent generation of defects such as breaking of circuit patterns. However, when a multi-layer board is manufactured by such methods, as with a conventional method of manufacturing multi-layer boards, thickness is increased because a multi-layer circuit board is manufactured by laminating a plurality of circuit boards with electronic parts built-in. In case of configuring a complicated circuit board, thickness tends to further increase because a number of laminated layers of circuit boards mounted with electronic parts is increased. Accordingly, it becomes difficult to reduce a thickness of the circuit board.